1. Field of the Invention
The invention generally relates to compositions and methods for the treatment of cancer with enzymes that deplete L-Methionine. More particularly, it concerns the engineering of a novel human methionine-γ-lyase enzyme with methionine degrading activity and greatly enhanced stability suitable for human therapy.
2. Description of Related Art
The demand for the essential amino acid, methionine, is exceptionally high in cancerous tissues. Depletion of methionine has been shown to be effective in killing a wide variety of tumor types without adversely effecting non-cancerous tissues. Methionine depletion can be effected via the action of enzymes that hydrolyze the amino acid. While human methionine depleting enzymes do not exist, a bacterial enzyme from Pseudomonas aeruginosa, methionine-γ-lyase, has been shown to be therapeutically effective in the clinic and has been evaluated in clinical trials. However, methionine-γ-lyase, as a bacterial protein, is highly immunogenic and elicits the formation of specific antibodies, leading to adverse reactions and reduced activity. Methionine-γ-lyase also has a very short half-life of only ˜2 hrs in vitro and in vivo, necessitating very frequent and impractically high dosing to achieve systemic depletion.
Systemic methionine depletion is the focus of much research and has the potential to treat cancers such as metastatic breast cancer, prostate, neuroblastoma, and pancreatic carcinoma among others. Although there is a lot of excitement for this therapeutic approach, the bacterially derived methionine-γ-lyase has serious shortcoming which greatly dampens enthusiasm for it as a chemotherapeutic agent.
Thus, there remains a need to develop methods and compositions to address these shortcomings for the therapeutic success of L-methionine depletion therapy.